1. Field of the Invention
This invention relates generally to semiconductor processing and, more specifically, to chemical vapor deposition processes for semiconductors. In particular, this invention relates to chemical vapor deposition of dielectric and other materials using organometallic precursors.
2. Description of the Related Art
With reduction in semiconductor device sizes and a corresponding increase in circuit complexity, the need has grown for reliable dielectric materials having high dielectric constants. Traditionally, silicon-based dielectrics, such as silicon dioxide (SiO2) and silicon nitride (Si3N4), have been used to form insulating layers in semiconductor devices, including dynamic random access memory chips (DRAMs). These silicon-based materials have been popular because they exhibit low current leakage and a high resistance to breakdown. However, these materials may not possess dielectric constants that are sufficiently high to meet the design requirements for more advanced semiconductor devices.
To meet the need for insulating material having a high dielectric constant, various alternatives to silicon-based dielectric materials have been suggested. However, these alternatives have not proved satisfactory due to shortcomings of one kind or another. For example, titanium dioxide (TiO2) has a high dielectric constant but also has a relatively high current leakage compared to SiO2 and Si3N4. Consequently, TiO2 is typically unsuitable for use in high density semiconductor devices due to the adverse effects of current leakage.
Recently, mixed phase TiO2 and SiO2 has been deposited from titanium tetrachloride (TiCl4), silane (SiH4) and nitrous oxide (N2O) using a plasma chemical vapor deposition (plasma CVD) technique. The object of this technique is to create a dielectric film having a relatively high dielectric constant as compared to SiO2 and a relatively low current leakage as compared to TiO2. However, this method has several drawbacks and fails to provide a satisfactory dielectric insulating layer for high density semiconductor devices. The use of TiCl4 as a titanium source results in the formation of chlorine related impurities in the dielectric film. These impurities are undesirable because chlorine has many adverse qualities, including being an etchant to SiO2, as well as being corrosive. In addition, the use of plasma CVD limits the range of applications for which this dielectric material may be used. Although plasma CVD methods may be employed at lower temperatures than traditional non-plasma methods, they typically produce poor step coverage when used to coat high aspect ratio devices. Therefore, this method does not reliably produce conformal films and thus, is not typically suitable for use in manufacturing modern high aspect ratio devices, such as DRAMs. The use of plasma deposition techniques is also known to create damage centers which induce high leakage in deposited dielectric films. Plasma processes also tend to incorporate hydrogen and other contaminants into the film, thereby further degrading quality and performance of semiconductor devices.
In other recently developed methods, organometallic precursors have been used in metal organic chemical vapor deposition (MOCVD) processes to deposit conductive layers, such as TiN and mixtures of TiSi2. In the conductor deposition processes, a liquid organometallic precursor is typically vaporized and carried into the reactor using a carrier gas. In the reactor the precursor reacts with another gaseous component, such as SiH4, nitrogen fluoride (NF3), or ammonia (NH3), to form conductive films on semiconductor surfaces. However, MOCVD processes have not been used for depositing multi-component oxide materials such as mixed phase titanium silicon oxide dielectrics.